A deep UV LED using diamond semiconductor has been developed by National Institute of Advanced Industrial Science and Technology of Japan (AIST), with the details of the development planned to be disclosed at the 56th Spring Meeting of the Japan Society of Applied Physics taking place from March 30.

The new deep UV LED uses a p-i-n-structured diamond semiconductor stacked on the 2mm-square diamond substrate, emitting deep ultraviolet light of 235nm wavelength, with output of 30μW under a current of 320mA.

There are two important characteristics of this new LED according to AIST. Firstly, its luminous efficiency continues to increase even under a large current, secondly, it can well resist high temperatures. Specifically speaking, with a current of a density exceeding 2,000A/cm2 through a 120μm-diametered electrode, the diamond LED still can have its luminous efficiency increasing without being saturated, according to AIST. As to the excellent heat resistance, even when temperature rises to 420°C, the light emission intensity of the LED does not degrade but continues to increase, AIST said.

The diamond LED emits light because of the generation of "excitons." For general LEDs, the excitons is vulnerable to heat and often deteriorates quickly, while the excitons generated in the diamond LED are very stable and will not break until 600°C, which is the major reason of its excellent temperature resistance.

At present, the commercialization of diamond LEDs is limited by the expensive price of the diamond substrate, with the available diamond substrates usually to be several square millimeters in size.

To solve this problem, AIST said they have been developing a technique to stack a polycrystalline diamond semiconductor film on a Si wafer, with the prototype formed with the new technique having efficiency only an order of magnitude lower than the currently developed diamond LED. "Because it only requires quite common materials such as silicon and methane, when the technique becomes practical, diamond LEDs can be produced at a very low cost."